This project will determine the relationship of humoral endorphin secretion to the normal sleep-wake cycle, daytime alertness/sleepiness and the pathophysiology of narcolepsy. Secretion patterns of humoral endorphin will be measured over 18 hours, including nocturnal sleep, in normal and narcoleptic groups. The periodicity, phase and amplitude of these secretion patterns will be related to nocturnal sleep patterns, daytime alertness/sleepiness, and pupillary size and reflex activity. Additionally, the possibility of excess endogenous opioids in narcolepsy will be examined by studying the effects of naloxone on pupils of normals and narcoleptics. Narcoleptics characteristically have miotic pupils. If naloxone reverses this miosis, it would indicate an excess of endogenous opioids. A normal response to naloxone administration would be no change or minimal miosis. The results of this study will make a major contribution to the elucidation of control mechanisms of the normal sleep-wake cycle and the neurochemical lesion of narcolepsy. Methods. Subjects will be 10 well-defined narcoleptics and 10 age-matched normal controls. Each subject will have 2 consecutive all-night sleep recordings. During the second night and following day, 10 cc. of blood will be drawn every 20 minutes beginning just before lights out and continuing for about 18 hours. Beginning in the morning, subjects will undergo daytime alertness/sleepiness procedures, including subjective alertness questionnaires, infrared electronic TV pupillometry and the Multiple Sleep Latency Test at 2-hour intervals until 5 sessions have been completed. All blood will be analyzed with a radioimmunoassay for humoral endorphin. All subjects will return within 1 week for the naloxone-Pupil Test. Following baseline pupillometry, 0.8 mg. of naloxone will be administered IM. Pupillometry will be repeated 5 minutes later and every 15 minutes thereafter for 2 hours. Pupillary dilation if found will indicate that the naloxone has antagonized endogenous opioids.